Numerical – 3. A certain sound has a frequency of 256 hertz and wavelength of 1.3 m. Calculate the speed with which this sound travels. What difference would be felt by a listener between this sound and another sound traveling at the same speed but of wavelength 2.6 m.

Numerical – 5. Radio waves of speed 3 × 108 m s-1 are reflected off the moon and received back on the earth, the time elapsed between the sending of the signal and receiving it back on the earth’s surface is 2.5 seconds. What is the distance of the moon from the earth?

Numerical – 7. A pendulum has a frequency of 5 vibration per second. An observer starts the pendulum and fires a gun simultaneously. He hears the echo from the cliff after 8 vibrations of the pendulum. If the velocity of sound in air is 340 m s-1, what is the ×distance between the cliff and the observer?

Numerical – 9. A radar is able to detect the reflected waves from an enemy aeroplane, after a time interval of 0.20 milliseconds. If the velocity of the waves is 3 × 108 m s-1, calculate the distance of the plane from the radar.

Numerical – 10. A man standing in front of a vertical cliff fires a gun. He hears the echo after 3 seconds. On moving closer to the cliff by 82.5 m, he fires again. This time, he hears the echo after 2.5 seconds. Calculate :